1. Field of the Invention
The present invention relates to the conversion of methane to higher hydrocarbons. In particular, the invention relates to oxidative conversion of methane to higher hydrocarbons by contacting a mixture of methane and a gaseous oxidant with a catalyst contact solid which does not contain a reducible metal oxide, the improvement being that the conversion is carried out in the presence of a chalcogen promoter.
2. Description of the Prior Art
Methane is found in large quantities in gaseous form in somewhat remote regions of the world. The transportation of this methane to areas where it can be utilized is relatively inefficient.
Considerable work has been carried out relating to the conversion of methane to higher molecular weight hydrocarbons which are readily condensable and which can be conveniently transported in liquid form. In this regard, reference is made to the following U.S. patents which are concerned with conversion of methane to higher hydrocarbons: U.S. Pat. Nos. 4,443,649; 4,444,984; 4,443,648; 4,443,645; 4,443,647; 4,443,644; 4,443,646; 4,499,323; 4,499,324; 4,593,139; 4,489,215; 4,499,322; 4,495,374; 4,544,784; 4,544,785; 4,547,610; 4,547,611; 4,517,398; 4,544,787; 4,547,608; 4,544,786; 4,568,785; 4,523,049; 4,523,050 and the like.
The oxidative conversion of methane to higher hydrocarbons can be carried out using solid contact agents which contain reducible metal oxides in both the redox mode, wherein the contact agent is alternately contacted with methane and oxidizing gas, and in the cofeed mode wherein the contact agent is contacted with a mixture of methane and gaseous oxidant. Redox mode operation is illustrated, for example, in U.S. Pat. Nos. 4,443,649; 4,444,984; 4,443,648; 4,443,645; 4,443,647; 4,443,644; and 4,443,646. Cofeed mode operation is illustrated, for example, in U.S. Pat. No. 4,523,049; 4,523,050 and 4,634,800.
In systems wherein reducible metal oxides are employed as an essential component of the contact solid, the use of chalcogen additives has been taught for operation in both redox and cofeed mode; see U.S. Pat. No. 4,544,785 and 4,670,619 respectively.
The oxidative conversion of methane to higher hydrocarbons can also be carried out in the cofeed mode using solid catalyst contact agents which are of a nonacidic nature and which do not contain reducible metal oxide as an active component. See, for example, copending applications Ser. Nos. 738,110 and 738,114, each filed May 24, 1985 the contents of which are incorporated herein by reference and made part hereof. See also published European Patent Applications Nos. 0196541 and 0198251 which are based on U.S. applications Ser. Nos. 713,653 and 713,652 respectively, each filed Mar. 19, 1985. In these later references there is provided the teaching that it is desirable to remove hydrogen sulfide from methane-containing feed gas prior to oxidative conversion.
Despite significant advances in the art of oxidative conversion of methane to higher hydrocarbons, a disadvantage has been the general decline in activity and selectivity achieved with various contact agents over time.